As conjunctions, although and though are interchangeable. Although is generally considered more formal than though, though both forms appear regularly in both formal and informal writing.
Though is also an adverb meaning however or nevertheless. In this sense, though is not interchangeable with although, which is only a conjunction.
In these examples, although and though are the same:
Growth in Europe is maintaining momentum, although the risks related to peripheral economies have increased. [Globe and Mail]
Unlike the other comparisons, however, this one is apt, though perhaps not in a way Cantor intended. [Washington Post]
Although the birds are just a small part of his business, carefully raising the pheasants from delicate eggs to beautifully feathered birds is clearly a passion. [The Age]
Some grown unschoolers, though positive about it overall, admit they’ve at times longed to be just like the other kids … [National Post]
And in these examples, though is an adverb and hence not interchangeable with although:
This weekend, though, theaters were packed. [Los Angeles Times]
There was another twist to come, though, as Pavlyuchenkova defied her flagging fortunes to win three games in succession. [Independent]